Although it will become evident to those skilled in the art that the present invention is applicable to a variety of implantable medical devices utilizing pulse generators to stimulate selected body tissue, the invention and its background will be described principally in the context of a specific example of such devices, namely, cardiac pacemakers or defibrillators for providing precisely controlled stimulation, cardioversion or defibrillation, pulses to the heart. The appended claims are not intended to be limited, however, to any specific example or embodiment described herein.
Implantable pacemaker or defibrillation leads form the electrical connection between the implanted cardiac pacemaker pulse generator or defibrillator and the heart tissue which is to be stimulated. As is well known, the leads connecting such pacemakers with the heart may be used for stimulation or for sensing electrical signals produced by the heart or for both stimulation and sensing in which case a single lead serves as a bi-directional pulse transmission link between the pacemaker and the heart. A transvenous endocardial type lead, that is, a lead which is inserted into a vein and guided therethrough into a cavity of the heart, includes at its distal end an electrode designed to contact the endocardium, the tissue lining the inside of the heart. The lead further includes a proximal end having a connector pin adapted to be received by a mating socket in the pacemaker. A flexible, coiled or wound conductor or cable surrounded by an insulating tube or sheath couples the connector pin at the proximal end with the electrode at the distal end.
For a Single-pass Atrial/Ventricular (SPAV) lead, the lead is intended to be placed with its distal tip in the right ventricle or in veins overlying the left ventricle, for stimulation and sensing in both ventricles and atria. On a typical bipolar SPAV lead, at minimum, there are typically two sets of electrodes. The first set of two electrodes is located at the distal tip for ventricular stimulation and sensing. The second set of two electrodes would be located in the atrium and proximally from the ventricular electrodes for atrial stimulation and sensing. Due to different sizes of hearts, it is difficult to determine a distance between the first and second set of the electrodes. Picking the wrong distance can result in the atrial electrodes being in a less optimal location in the atrium or ventricle, further resulting in insufficient stimulation and/or sensing performance. One of the current solutions is to have more than one set of electrodes on the lead body. Each set of the electrodes is connected to a bipolar connector. At implant, the implanter would choose the proper set of the electrodes for that particular patient. This approach is acceptable but there is a huge drawback. At the end of the implant, the extra connectors of the unused electrode sets must be either cut-off or capped-off. In order to solve the problem of having the extra connectors, the invention described below will provide a method of using only one connector, which could work with two or more sets of the electrode pairs.
Typical of prior art disclosures is U.S. Pat. No. 5,919,222 to Hjelle et al. which discloses an adjustable medical electrode lead with a wide degree of adjustability and flexibility with regard to the locations and length of its cardioversion/defibrillation electrodes. This is accomplished by means of a single elongated defibrillation electrode over which one or more sliding sheaths is located, each of the sheaths having a length less than that of the electrode itself. By this mechanism, movement of the sheath or sheaths relative to the electrode can be used to provide for single or multiple electrode surfaces and to vary the location and length of those surfaces along the length of the lead.
U.S. Pat. No. 5,584,874 to Rugland et al. discloses a medical electrical lead with an anchoring sleeve having a series of circumferential suture grooves at longitudinally spaced locations to accommodate different sizes of patients.
U.S. Pat. No. 5,578,067 to Ekwall et al. discloses an electrode apparatus with which the distance between the electrodes on an electrode cable can be changed in a very simple manner and in which the surface area exposed to tissue of at least one electrode can be enlarged, reduced and even rotated around the electrode cable in certain instances.
U.S. Pat. No. 4,602,645 to Barrington et al. discloses a cardiac pacing catheter system which includes a main guiding catheter and a pair of electrical leads adapted to make direct electrical contact with the ventricle and the atrium of the patient's heart. Each of the leads can be advanced and manipulated separately within the main catheter body to accommodate different sizes of hearts.
U.S. Pat. No. 5,578,067 to Ekwall et al. discloses a single-pass atria-ventricular lead for transvenous insertion. An adjustment device to accommodate the size of the patient is provided to allow axial adjustment of the ventricular lead sheath relative to the atrial lead sheath without modification to or adjustment of the connector assembly prior to attachment of an implantable pulse generator.
It was in light of the foregoing that the present invention was conceived and has now been reduced to practice.